1. Field of the Invention
This invention relates to a novel laundry detergent composition having a high water-soluble alkaline carbonate builder content, the use of which results in reduced fabric encrustation due to delayed release of a polymeric polycarboxylate present in the composition.
2. Information Disclosure Statement Including Description of Related Art
The following information is being disclosed under the provisions of 37 CER 1.56, 1.97 and 1.98.
Laundry detergent compositions comprising a water-soluble alkaline carbonate are well-known in the art. For example, it is conventional to use such a carbonate as a builder in detergent compositions which supplement and enhance the cleaning effect of an active surfactant present in the composition. Such builders improve the cleaning power of the detergent composition, for instance, by the sequestration or precipitation of hardness causing metal ions such as calcium, peptization of soil agglomerates, reduction of the critical micelle concentration, and neutralization of acid soil, as well as by enhancing various properties of the active detergent, such as its stabilization of solid soil suspensions, solubilization of water-insoluble materials, emulsification of soil particles, and foaming and sudsing characteristics. Other mechanisms by which builders improve the cleaning power of detergent compositions are probably present but are less well understood. Builders are important not only for their effect in improving the cleaning ability of active surfactants in detergent compositions, but also because they allow for a reduction in the amount of the surfactant used in the composition, the surfactant being generally much more costly than the builder.
Two important classes of builders have been widely used in recent years, viz., phosphorus containing salts such as sodium tripolyphosphate (STPP) which are very effective in sequestering calcium and magnesium ions without precipitating them, and the water-soluble alkaline carbonates mentioned previously such as sodium carbonates which may be used in amounts up to 90 wt. % of the composition and which effectively precipitate the calcium ions. However, phosphorus-containing builders have been found to cause a serious problem of eutrophication of lakes, rivers and streams when present in detergent compositions in relatively large amounts, resulting in the passage of laws in several states mandating a drastic reduction in their use. While the use of water-soluble alkaline carbonate builders do not cause eutrophication, they result in the unrelated problem of calcium carbonate precipitation, leading to, for example, fabric encrustation due to the deposition of the calcium carbonate on the fiber surfaces of fabrics which in turn causes fabric to have a stiff hand and gives colored fabrics a faded appearance.
Polymeric polycarboxylates such as polyacrylates are also known in the detergent art as effective sequestering and dispersing agents as well as crystal growth inhibitors. As a result of these properties, the presence of a polymeric polycarboxylate in a high carbonate detergent composition has the known effect of reducing the redeposition of soil and encrustation of calcium carbonate on the surfaces of fabrics washed with such high carbonate detergents. However, a problem connected with the use of such polycarboxylates is that they have limited biodegradability which presents an environmental problem if they are used in relatively large amounts. In the light of these factors, any expedient connected with the use of a satisfactorily small amount of polymeric polycarboxylate which results in an enhanced reduction of fabric encrustation as well as the expected reduction of soil redeposition, is very desirable.
The following prior art references may be considered relevant or material to the invention claimed herein.
U.S. Pat. No. 4,265,790, issued May 5, 1981 to Winston et al., and U.S. Pat. No. 4,464,292, issued Aug. 7, 1984 to Lengyel, disclose detergent compositions comprising an ethoxylated alcohol and an ethoxy sulfate as a combination of nonionic and anionic surfactants, and over 70 wt % of anhydrous sodium carbonate (soda ash) as a detergent builder.
U.S. Pat. No. 4,490,271, issued Dec. 25, 1984 to Spadini et al., discloses detergent compositions comprising an active surfactant, up to 80% of a non-phosphorus detergent builder such as a water-soluble carbonate, and a polyacrylate such as a copolymer of acrylic acid with any of various comonomers.
U.S. Pat. No. 4,521,332, issued Jun. 4, 1985 to Milora, discloses highly alkaline liquid cleaning compositions comprising a nonionic surfactant, 10 to 45 wt. % of sodium hydroxide, 0.04 to 4 wt. % of a polyacrylic acid salt, 0 to 15 wt. % of an alkali metal phosphate builder such as STPP, 0.5 to 20 wt. % of a "building agent" such as sodium carbonate, and 6 to 60 wt. % of water.
U.S. Pat. No. 4,711,740, issued Dec. 8, 1987 to Carter et al., discloses detergent compositions comprising a "detergent active" compound, i.e., a surfactant, a detergent builder which is a water-soluble carbonate, e.g. sodium carbonate in an amount of "at least 5% by weight, such as from 10% to 40%, preferably 10% to 30% weight, though an amount up to 75% could possible be used if desired in special products," a water insoluble carbonate, e.g., calcium carbonate (calcite) in an amount of 5 to 60 wt. %, as seed crystals for precipitated calcium carbonate which is thus prevented from being deposited on fabrics; and a copolymer of a carboxylic monomer, e.g., acrylic acid, and a non-carboxylic monomer, such copolymer being present in an amount of 0.1 to 10 wt. % and acting as a colloid stabilizer for the precipitated calcium carbonate.
U.S. Pat. No. 4,820,441, issued Apr. 11, 1989 to Evans et al., discloses granular detergent compositions which may contain in addition to an active surfactant, 5 to 75 wt. % of a crystal growth modified, carbonate-based structurant salt, 0.1 to 20 wt. % of a polymeric polycarboxylate as crystal growth modifier based on the weight of the structurant salt, and 0 to 40 wt. % of STPP. The structurant salt may contain sodium sulfate as well as sodium carbonate and sodium bicarbonate, and the two tables under the heading "PRODUCTS OF THE INVENTION" in columns 8 and 9 of the patent show a maximum of 40 wt. % of sodium carbonate in the final product composition.
U.S. Pat. No. 4,849,125, issued Jul. 18, 1989 to Seiter et al., discloses phosphate-reduced, granular, free-flowing detergent compositions comprising 4 to 40 wt. % of a nonionic surfactant, 3 to 20 wt. % of an anionic surfactant, 0.5 to 15 wt. % of a homopolymeric or copolymeric carboxylic acid or salt, 0 to 20 wt. % of STPP, and, optionally, up to 15 or 20 wt. % of sodium carbonate.